Fig. 2

a, c, e SEM and b, d, f TEM images of Mn₃O₄ sample (a, b), original MnO-600 catalyst (c, d) and the correspondingly tested MnO-600 catalyst for 2000 ORR cycles (e, f). g, h Spherical aberration-corrected TEM (g) and TEM-EDS elemental mappings (h) images of MnO-600 sample